The description does not say anything about "Special Edition" and the release date of 2019 (instead of 2021) implies that it is not. However, the system requirements state that "Skyrim Special Edition" needs to be owned on GOG. This implies that it is.

Steam has them both:

https://store.steampowered.com/app/933480/Enderal_Forgotten_Stories/

https://store.steampowered.com/app/976620/Enderal_Forgotten_Stories_Special_Edition/

I am confused as well. The store page says 2019 but the System Reqs say "Skyrim Special Edition needs to be owned on GOG but it does not have to be installed to run the mod". And it installs and runs with Skyrim SE version.

So which version is it?

Having done a bit of research, I believe this is the Enderal Special Edition (SE).

Indications:

- The game installs into a path named Enderal Special Edition GOG
- It uses SKSE64 which is the Skyrim Script Extender for the SE version
- Plugins like EnderalSE.dll, SSEDisplayTweaks.dll und SkyrimRedirector.dll are only compatible with Skyrim SE
- The file SkyUI_SE_GERMAN.txt is the SE version of the SkyUI menus
- The game installs and runs with the Skyrim SE version

The fact that it says ‘2019’ on the shop page may only be a description of the content - technically and functionally it seems to be the SE version from 2021 or newer.